The great number of patents issued in the field of weightlifting equipment evidences the popularity of this type of exercise as a way to stay in shape or improve physical conditioning. Also, the variety of equipment invented and patented shows that there is a desire to go beyond the basic barbell and circular weight plates, also known as "free weights". A principal drawback associated with the use of free weights is that, when the lifter is working out with a weight amount at or near his "maximum", he is less capable of controlling and balancing the bar, thereby making the exercise unsafe unless one or more spotters (other weight lifters) are used. Weight lifting machines solve the control and balance problems in most instances, thereby making it safe for the lifter to perform the exercise without the need for spotters.
A primary concern in the design of weightlifting machines is providing the apparatus with a weight or set of weights to be used in performing the exercise. This becomes especially important if the machine is designed to allow a lifter to perform more than one type of exercise. It is well known that certain muscle groups of the body are capable of working against greater weights than others. Therefore, a machine must be capable of providing proper ranges of weight for all of the different exercises. An example of this situation is found in U.S. Pat. No. 4,407,495, issued to Wilson. This machine is capable of allowing the lifter to perform the bench press, shoulder or military press, various pulling exercises, and leg extensions. The problem of providing different weights required for the various exercises is solved in this machine by resorting to the use of free weight plates, and further allowing the position of the transverse bar holding the weights to be adjusted as necessary.
Although this machine avoids the control and balance problems previously mentioned as being associated with the use of a barbell, other undesirable features associated with the use of free weight plates in conjunction with exercise machines become evident here. First, a resonably extensive set of weight plates is required to allow various combinations of plates to be used in selecting the proper weight for a given exercise. The weight plates must be evenly distributed on either side of the exercise bar in order for proper operation at the pivot point of the machine. Additionally, many times plates weighing as much as 25 or 50 pounds (or standard metric weights, such as 100 kg) are used, and must be lifted from the ground into position onto the bar adapted to hold them
Other types of machines, either of the single exercise type or multi-exercise type, employ a stack of plates disposed to be lifted along vertical guide elements. U.S. Pat. No. 3,905,599, issued to Mazman, is an example. The total amount of weight in the weight stack is determined by the equipment designer, and in general the designer attempts to provide sufficient weight for even the stronger members of the general public who might wish to use the equipment. The weight to be used in the exercise is selected by inserting a pin through an opening in a particular plate and through a cylindrical rod running vertically through the weight stack which has bores in alignment with the weight plate openings when the machine is at a rest position. In the machine shown in the Mazman patent, all weight plates above and including the pinned plate will be the ones which will be raised and lowered during the exercise.
While it would appear that this arrangement makes weight selection very simple, there are some not-so-apparent drawbacks which can frequently be evidenced in health clubs and weight training rooms where these machines are used by a wide assortment of individuals. The use of these plates requires that the weight selection be done in discrete increments. The weight plates most commonly used in these machines weigh ten pounds, and for machines designed for exercises requiring greater weight such as leg press machines, twenty-five pounds is the common size. The use of such increments inhibits the ability of a lifter to increase muscle strength consistently because the lifter is required to increase his maximum exercise weight in these large increments. It is very difficult to make such large jumps when the lifter is advancing beyond his or her personal maximums.
Frequently, one will see a lifter in a weight room improvise to avoid this problem by hanging a five-pound plate taken from the "free weight" plate assortment around the exposed end of a pin which has been inserted into the weight stack at a selected location. This allows the lifter to progress at five-pound increments on a ten-pound plate machine. Ten-pound free weight plates are frequently used in the same manner on machines having twenty-five pound increments. The pins are not usually long enough to hold more than one extra free weight plate and still operate properly. Thus, a lifter wishing to exercise with, for example, 471/2 pounds of weight on a machine having 10-pound increments may or may not be able to hang a five-pound and a 21/2 pound weight from a pin inserted at the 40-pound plate. The occurrence of this is frequent enough that devices have actually been developed which attach to the top plate of a stack and come in 21/2, 5, and 10 pound increments.
A further disadvantage of weight stacks of this type is that if the desired smaller increments are provided in the stack, the number of plates must be correspondingly increased. Because the various sizes of this type of weight plate all have roughly the same height (changes in the length and width primarily accounting for the weight difference), it might not be possible to provide a sufficient number of plates on the machine for the stronger lifters to perform the exercise at a preferred weight. This situation would also arise in the multi-exercise machines using weight stacks having plates of smaller increments, wherein the weight stack may not have sufficient total weight for all of the various exercises.
One example of an exercise machine having an essentially continuous range of weight selections is seen in U.S. Pat. No. 3,573,865 issued to Annas et al. This machine, however provides a very complex, cumbersome and expensive arrangement for providing the continuous selection range. An electric motor is provided with threaded rod for moving a block along a rail element to adjust the position of the block relative to a pivot point.
It is therefore an important object of the present invention to provide a weightlifting exercise machine which provides a substantially continuous range of weight selections for performance of an exercise, ranging from very small exercise loads to large exercise loads.
It is a further important object of the present invention to provide a weightlifting exercise machine which provides a substantially continuous range of weight selections while at the same time is very easy to adjust and is low in cost.
It is a further important object of the present invention to provide a weightlifting exercise machine which is capable of allowing a user to perform more than one type of exercise which will permit the exercise of different muscle groups in the body.
It is a further important object of the present invention to provide a weightlifting exercise machine which has a heavy primary weight member and an adjustable heavy secondary weight member, the secondary member being capable of being positioned either to add substantial weight to the primary weight or to counterbalance much of the primary weight, or positioned anywhere between these two extreme positions.